I would certainly change the mechatronic sleeve while you have transmission open. Changing it won't help with the operation of the transmission in any way but it will fix or avoid a fluid leak, which is bad for your transmission.
I also doubt that just a fluid change will fix your hard 2-1 shift, going by what others have said on here and on other forums for cars that use the ZF 6HP26. I has helped in some cases but not in most.
Some folk have have good results with the fluid change along with a new bridge seal and new jumps seals. One again, while you are in there, why not replace them...?
Others have flashed (or re-flashed) the firmware in the transmission control unit with good results.
I think ultimately it's either new solenoids or a new (or refurbished) mechatronic unit that is the cure.
But it really depends on what exactly is wrong in your transmission and so while there are many seemingly common issues, the causes can vary and so must the action taken to remedy the problem.
Changing the fluid and seals is the first step to finding out I suppose!
